/*
 * Copyright (c) 2007-2012, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package com.sun.org.apache.bcel.internal.util;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache BCEL", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import java.util.Hashtable;
import java.io.*;
import com.sun.org.apache.bcel.internal.*;
import com.sun.org.apache.bcel.internal.classfile.*;

/**
 * <p>Drop in replacement for the standard class loader of the JVM. You can use it
 * in conjunction with the JavaWrapper to dynamically modify/create classes
 * as they're requested.</p>
 *
 * <p>This class loader recognizes special requests in a distinct
 * format, i.e., when the name of the requested class contains with
 * "$$BCEL$$" it calls the createClass() method with that name
 * (everything bevor the $$BCEL$$ is considered to be the package
 * name. You can subclass the class loader and override that
 * method. "Normal" classes class can be modified by overriding the
 * modifyClass() method which is called just before defineClass().</p>
 *
 * <p>There may be a number of packages where you have to use the default
 * class loader (which may also be faster). You can define the set of packages
 * where to use the system class loader in the constructor. The default value contains
 * "java.", "sun.", "javax."</p>
 *
 * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
 * @see JavaWrapper
 * @see ClassPath
 */
public class ClassLoader extends java.lang.ClassLoader {
    private Hashtable classes = new Hashtable(); // Hashtable is synchronized thus thread-safe
    private String[] ignored_packages = { "java.", "javax.", "sun." };
    private Repository repository = SyntheticRepository.getInstance();
    private java.lang.ClassLoader deferTo = ClassLoader.getSystemClassLoader();

    public ClassLoader() {
    }

    public ClassLoader(java.lang.ClassLoader deferTo) {
        this.deferTo = deferTo;
        this.repository = new ClassLoaderRepository(deferTo);
    }

    /** @param ignored_packages classes contained in these packages will be loaded
     * with the system class loader
     */
    public ClassLoader(String[] ignored_packages) {
        addIgnoredPkgs(ignored_packages);
    }

    public ClassLoader(java.lang.ClassLoader deferTo, String[] ignored_packages) {
        this.deferTo = deferTo;
        this.repository = new ClassLoaderRepository(deferTo);

        addIgnoredPkgs(ignored_packages);
    }

    private void addIgnoredPkgs(String[] ignored_packages) {
        String[] new_p = new String[ignored_packages.length + this.ignored_packages.length];

        System.arraycopy(this.ignored_packages, 0, new_p, 0, this.ignored_packages.length);
        System.arraycopy(ignored_packages, 0, new_p, this.ignored_packages.length, ignored_packages.length);

        this.ignored_packages = new_p;
    }

    protected Class loadClass(String class_name, boolean resolve) throws ClassNotFoundException {
        Class cl = null;

        /* First try: lookup hash table.
         */
        if ((cl = (Class) classes.get(class_name)) == null) {
            /* Second try: Load system class using system class loader. You better
             * don't mess around with them.
             */
            for (int i = 0; i < ignored_packages.length; i++) {
                if (class_name.startsWith(ignored_packages[i])) {
                    cl = deferTo.loadClass(class_name);
                    break;
                }
            }

            if (cl == null) {
                JavaClass clazz = null;

                /* Third try: Special request?
                 */
                if (class_name.indexOf("$$BCEL$$") >= 0)
                    clazz = createClass(class_name);
                else { // Fourth try: Load classes via repository
                    if ((clazz = repository.loadClass(class_name)) != null) {
                        clazz = modifyClass(clazz);
                    } else
                        throw new ClassNotFoundException(class_name);
                }

                if (clazz != null) {
                    byte[] bytes = clazz.getBytes();
                    cl = defineClass(class_name, bytes, 0, bytes.length);
                } else
                    // Fourth try: Use default class loader
                    cl = Class.forName(class_name);
            }

            if (resolve)
                resolveClass(cl);
        }

        classes.put(class_name, cl);

        return cl;
    }

    /** Override this method if you want to alter a class before it gets actually
     * loaded. Does nothing by default.
     */
    protected JavaClass modifyClass(JavaClass clazz) {
        return clazz;
    }

    /**
     * Override this method to create you own classes on the fly. The
     * name contains the special token $$BCEL$$. Everything before that
     * token is consddered to be a package name. You can encode you own
     * arguments into the subsequent string. You must regard however not
     * to use any "illegal" characters, i.e., characters that may not
     * appear in a Java class name too<br>
     *
     * The default implementation interprets the string as a encoded compressed
     * Java class, unpacks and decodes it with the Utility.decode() method, and
     * parses the resulting byte array and returns the resulting JavaClass object.
     *
     * @param class_name compressed byte code with "$$BCEL$$" in it
     */
    protected JavaClass createClass(String class_name) {
        int index = class_name.indexOf("$$BCEL$$");
        String real_name = class_name.substring(index + 8);

        JavaClass clazz = null;
        try {
            byte[] bytes = Utility.decode(real_name, true);
            ClassParser parser = new ClassParser(new ByteArrayInputStream(bytes), "foo");

            clazz = parser.parse();
        } catch (Throwable e) {
            e.printStackTrace();
            return null;
        }

        // Adapt the class name to the passed value
        ConstantPool cp = clazz.getConstantPool();

        ConstantClass cl = (ConstantClass) cp.getConstant(clazz.getClassNameIndex(), Constants.CONSTANT_Class);
        ConstantUtf8 name = (ConstantUtf8) cp.getConstant(cl.getNameIndex(), Constants.CONSTANT_Utf8);
        name.setBytes(class_name.replace('.', '/'));

        return clazz;
    }
}
